We are characterizing three classes of nuclear RNA protein-complexes which react with autoimmune antibodies occurring in the systemic rheumatic diseases. The protein moieties of the three types of complexes are relatively well characterized. They consist of a polypeptide of molecular weight 13,000 (p 13), a polypeptide of molecular weight 70,000(Sc1-70) and histone H1, respectively. P 13-RNA complexes react with antibodies occurring in mixed connective tissue disease (MCTD). Sc1-70 and H1-RNA complexes react with antibodies seen in scleroderma and systemic lupus erythematosus (SLE), respectively. Having defined the protein compositions of the complexes we now propose to characterize the RNA. The antigenic complexes will be isolated from Friend leukemia cell nuclei which have been radiolabeled in vivo with 3H- uridine or 32p. Protocols for isolating the antigenic complexes have been described previously (Douvas et al, 1979, J. Biol Chem. 254:3608-3616 and J. Biol Chem. 254:10514-10522). We will then extract the RNA and electrophorese it on polyacrylamide gels. The gels will be analyzed by autoradiography. Preliminary results indicate that each type of complex contains a few discreet RNA species. Each species will be further characterized by two-dimensional fingerprinting and sequencing. We are also investigating an enzymatic activity associated with Sc1-70. Preliminary results indicate that this protein is a polynucleotide kinase.